Thursday, 1 December 2016

Does Age make us sage or sag?

If you are of sensitive disposition, and certainly if you are over 60 years of age, look away now. Age is not good news for the thinking person. The results can be summarised in one word: decline. If you protest that I have been too brief, I can triple the word count: decline and fall.

Can we find more appealing results by taking another large sample, and applying more extensive measures of mental ability?

Background: Populations worldwide are aging. Cognitive decline is an important precursor of dementia, illness and death and, even within the normal range, is associated with poorer performance on everyday tasks. However, the impact of age on cognitive function does not always receive the attention it deserves.

Methods:

We have explored cross-sectional associations of age with five cognitive tests (word recall, verbal fluency, subtraction, number sequence, and numerical problem solving) in a large representative sample of over 40,000 men and women aged 16 to 100 living in the UK.

Results:

Women performed better on word recall tests and men had higher scores for subtraction, number sequence and numerical problem solving. However, age-cognition associations were generally similar in both genders. Mean word recall and number sequence scores decreased from early adulthood with steeper declines from the mid-60s onwards Verbal fluency, subtraction and numerical problem solving scores remained stable or increased from early to mid-adulthood, followed by approximately linear declines from around age 60. Performance on all tests was progressively lower in respondents with increasingly worse self-rated health and memory. Age-related declines in word recall, verbal fluency and number sequence started earlier in those with the worst self-rated health. There was no compelling evidence for age dedifferentiation (that the general factor of cognitive ability changes in strength with age).

Conclusions:

We have confirmed previously observed patterns of cognitive aging

Sharp declines for word recall, verbal fluency and number sequences; declines after 60 years of age for numerical problem solving, and even some gradual decline on subtraction. Ironic, is it not, that after the subtraction of all our skills, subtraction itself should be spared?

Somewhat chastened by these findings, I turned to another paper in the hope it would cheer me up. Written by the same incredible Edinburgh gang, who have cornered the market in ageing research, they try to find what makes people age well from a cognitive point of view. Surely with a few mental exercises and a good helping of fresh vegetables all will be well with me?

I call these “the hedgehogs”. They show that if you give every ageing person the same starting point then they age at different speeds. This gives us all hope. It may be delusional hope, but it is hope nonetheless. What makes some of us age gracefully?

It is critical to discover why some people's cognitive abilities age better than others'. We applied multivariate growth curve models to data from a narrow-age cohort measured on a multi-domain IQ measure at age 11 years and a comprehensive battery of thirteen measures of visuospatial, memory, crystallized, and processing speed abilities at ages 70, 73, and 76 years (n= 1091 at age 70). We found that 48% of the variance in change in performance on the thirteen cognitive measures was shared across all measures, an additional 26% was specific to the four ability domains, and 26% was test-specific. We tested the association of a wide variety ofsociodemographic, fitness, health, and genetic variables with each of these cognitive change factors. Models that simultaneously included all covariates accounted for appreciable proportions of variance in the cognitive change factors(e.g. approximately one third of the variance in general cognitive change). However,beyond physical fitness and possession of the APOEe4 allele, very few predictors were incrementally associated with cognitive change at statistically significant levels. The results highlight a small number of factors that predict differences in cognitive ageing, and underscore that correlates of cognitive level are not necessarily predictors of decline. Even larger samples will likely be required to identify additional variables with more modest associations with normal range heterogeneity in aging related cognitive declines.

The study has three waves of testing over six years (70 to 76 years of age), and a broad range of cognitive measures. It is also informed by the original measure of intelligence at age 11, so far better grounded than most research.

Here are the key findings:

If you want a really good test of decrement of ability for the over 70s, use Digit Symbol substitution. Better than a brain scan any day.

About half of the drop in function across the 13 cognitive measures is shared. “It all goes together when it goes” is at least half true.

Brighter children become brighter, healthier, and fitter older adults. This ‘preserved differentiation’ appeared to last into the eighth decade of life.

The most robust and consistent predictor of cognitive change within old age, even after control for all the other variables, was the presence of the APOEe4 allele. APOEe4 carriers showed over half a standard deviation more general cognitive decline compared to non-carriers, with particularly pronounced decline in their Speed and numerically smaller, but still significant, declines in their verbal memory.

Women had significantly less general cognitive decline than men, mainly centered on Crystallized ability.

No evidence for a relation between education (or social class) and the slope of any of the cognitive factors.

The three fitness indicators weren’t much related to the rate of cognitive decline, but taken together there was a higher correlation, but nothing in this study to test the idea that improving physical functioning would have had a cognitive sparing effect.

If you don’t like the general drift of these results you may wish to say that age is a social construct, that the definition of old age is arbitrary, that countries differ considerably in their classifications of the elderly, that there is no precise point at which a person becomes old and that the whole concept is meaningless, or indeed totally meaningless. You could also argue that people have many abilities which have not been measured by the particular tests used in these studies, and that those untested abilities probably show no decrements. For example, tuneless whistling, stirring coffee while meditating, the recollection of things past, and smiling faintly at the last but one joke in a conversation. Each person shows their genius in their own way.

Back to the results. Perhaps a younger reader would be willing to take a quick look at all of them to make sure that I have understood them properly.

On reflection, I would ask the young reader that if this complex task takes you only a moment, please delay for a while before responding to me, so as not to make the contrast in our processing speeds too evident.

I am only too aware of my cognitive decline. Once I was sharp: less so now. The aspect I particularly hate isn't narrowly cognitive: I have become occasionally clumsy. The combination of still having quick reflexes while no longer being adroit can be peculiarly destructive.

And there's another thing that frustrates, the decline in eyes and ears. It's a sad motto for old age: not deft but deaf.

The hedgehogs imply that any decline is lost in the noise, except for speed. Lots of people seem to get better scores as they age, mostly just because of random variations and test limitations, no doubt, but it seems possible to improve on any of these factors by improving health, continuing practice and maybe some vitamins and drugs. The numbers seem almost like a different study. How can the variance of the slopes be so low when the hedgehogs look like that, with slopes all over the place? Maybe I don't get what variance is supposed to mean or be of in this case?